Picosecond fluorescence spectroscopy of purple membrane in Halobacterium halobium with a photon-counting streak camera

Abstract

Fluorescence lifetimes and spectra of native and deionized purple membranes of Halobacterium halobium at 22°C were measured to be <3 and 12±4 ps, respectively, with a photon-counting streak camera system. The results confirmed that the blue-shifted transient previously found by absorption spectroscopy is attributed to bacteriorhodopsin in the lowest excited-singlet state. Ultraweak fluorescence of the light-adapted purple membrane with 2.5 × 10 −4 quantum yield could be detected even though the excitation pulse energy at 570 nm was reduced to 0.88 pJ (72 μW average power).